1. Field of the Invention
The present invention concerns a metal pipeline having a protective coating layer for an automobile, which is excellent in heat resistance, corrosion resistance and impact resistance and used for transportation of fluids such as oils and fuels under severe corrosive circumstances.
2. Description of Prior Arts
For preventing damage to brake oil or fuel oil pipelines of an automobile disposed under the floor of a car body caused by popping pebbles or splashing mud, preventing damage caused by interference between pipelines and other parts in an engine room, or preventing damage caused by interference between tools or parts upon assembling parts, a coated pipe has been known which is manufactured by forming a zinc plating layer on the outer surface of a steel pipe, forming a chromate layer on the zinc plating layer and covering the chromate layer with an extruded thermoplastic resin such as nylon, polyethylene or polypropylene resin.
However, since the resin is extruded by using an extrusion molding machine upon coating an extruded thermoplastic resin, such a coated pipe suffers from a problem that hydrates contained in the chromate layer are evaporated by heating upon molding and the chromate layer shrinks to cause cracking in the layer, so that corrosion resistance is deteriorated remarkably, particularly, to a portion in which a substrate is exposed due to injury of the resin by the popping stones or like, to a portion in which the resin is peeled off for the fabrication of a pipe end or to a portion in which the resin is not covered during intermittent extrusion molding.